Jody Winslow, of Farmington, Conn., carries signs regarding the Second Amendment as he heads back to the Capitol building in Hartford, Conn., on Wednesday.

HARTFORD, Conn. — Calling the massacre last year at Sandy Hook Elementary School “the nation’s worst nightmare,” Connecticut lawmakers debated a wide-ranging package of gun control and other measures Wednesday that they were expected to pass over the outcry of gun rights advocates who gathered in protest at the Capitol.

Debate on the legislation, touted by supporters as the most comprehensive in the country, began Wednesday in the Senate. The state House of Representatives was expected to take up the proposal after the Senate’s anticipated approval.

“The tragedy in Newtown demands a powerful response, demands a response that transcends politics,” said Senate President Donald E. Williams Jr., a Brooklyn Democrat, calling the work the “culmination of a bipartisan effort” that included unprecedented public input.

Some of the measures would take effect right away, including the expansion of the state’s assault weapons ban, background checks for all firearms sales and a ban on the sale or purchase of ammunition magazines holding more than 10 rounds.

The bill also addresses mental health and school security measures, including $15 million to help pay for school security infrastructure upgrades.

“When a child is sent to school, their parents expect them to be safe. The Sandy Hook shooting rampage was a parent’s, a school system’s, a community’s and the nation’s worst nightmare,” said Republican state Sen. Toni Boucher of Wilton.

While Republican state Sen. John Kissel of Enfield acknowledged that “you just can’t have a heart at all if you don’t feel for the families and friends and neighbors of the victims of that Newtown massacre,” he expressed concern that the bill is ultimately harmful to lawful gun owners.

“When it comes to further regulations on guns and ammunition in one of the states that’s touted as having, right now, some of the most tough gun laws in the United States of America, I think it goes one step too far,” said Kissel, who planned to vote no.

Gun rights advocates greatly outnumbered gun control supporters who gathered at the statehouse in Hartford to witness the debate. Gun owners, some holding signs questioning the constitutionality of the proposals, stood in protest outside the state Capitol and a nearby building housing legislative offices. Many also packed the hallways outside the Senate chamber, occasionally chanting “No! No! No!” and “Read the bill!”

Police presence was heavier than usual and Gov. Dannel P. Malloy’s security detail decided to cancel an appearance by the governor — a vocal gun control proponent — at an event inside the state Capitol.

“We want them to write laws that are sensible,” said Ron Pariseau, 66, of Pomfret, who was angry he’ll be made a felon if he doesn’t register his weapons that will no longer be sold in Connecticut. “What they’re proposing will not stop anything.”

Dan and Lauren Garrett of Hamden, wearing green shirts in honor of the Sandy Hook victims, traveled to Hartford from their home in Hamden with their 10-month-old son, Robert, to watch lawmakers pass what they’ve called the strongest gun laws in the country.

Both hope lawmakers will build on the proposal.

“It’s just the beginning of this bill. In six months from now, it’s going to get stronger and stronger,” said Dan Garrett. “I think they’re watching us all over the country.”

Malloy, a Democrat, has said he’ll sign the legislation into law, even though it would allow people to keep their high-capacity magazines so long as they’re registered with the state by Jan. 1, 2014.

“You can make an argument, a strong argument, this is the toughest law passed anywhere in the country,” he said.

But gun rights advocates question whether the legislation would have done anything to stop Adam Lanza, the 20-year-old who blasted his way in to the Sandy Hook Elementary School in Newtown on Dec. 14. State police say he fired 154 shots with a Bushmaster .223-caliber rifle, gunning down 20 first-graders and six educators. He had earlier killed his mother, Nancy, and later committed suicide.

For some protesters, the mental health measures in the proposal were overshadowed by the gun control restrictions.

“I want to focus on people like Adam Lanza and the people that cause those mass killings,” said Richard Pieczarka, 69, a retiree from Coventry. “That’s the problem.”

Search warrants of the Lanzas’ Newtown home showed it was packed with weapons and ammunition.

“If it did something to prevent this incident, where the fault lies with the individual and the mother, not with the legitimate gun owners in this state, then we could probably support something,” said Robert Crook, executive director of the Coalition of Connecticut Sportsmen.